Tanycytes are specialized ependymal cells found in high density along the floor and ventrolateral walls of the third ventricle between the rostral and caudal limits of the hypothalamic median eminence. Little is known about these cells but their expression of type 2 iodothyronine deiodinase (D2), an enzyme critical for conversion of thyroid hormone into its active form, and responsiveness to fasting and endotoxin in several animal species, has raised the possibility that tanycytes are involved in energy homeostasis and contribute to the mechanism by which circulating thyroid hormone levels fall in individuals with severe infection, termed the "nonthyroidal illness syndrome". To facilitate understanding of the importance of tanycytes in neuroendocrine regulation through effects on the hypothalamic-pituitary-thyroid (HPT) axis and feeding-related centers in the arcuate nucleus, we propose to identify tanycytes-specific genes using laser capture microdissection and microarray analysis and develop transgenic mice that express Cre recombinase specifically in tanycytes. These mice will be used to develop a tanycyte cell culture system, and to specifically ablate alpha and/or beta n vivo by developing double transgenic mice after crossing with a Cre-inducible diphtheria toxin receptor mouse line. These studies are expected to generate new information about the biologic importance of tanycytes and their role in neuroendocrine regulation of the HPT axis and in energy homeostasis. PUBLIC HEALTH RELEVANCE: Tanycytes are specialized cells that line the floor and ventrolateral walls of the third ventricle. Compelling evidence suggests they have an important role in generating thyroid hormone due to high expression of type 2 iodothyronine deiodinase, an enzyme critical for conversion of the prohormone, T4, into the biologically active thyroid hormone, T3. We have proposed, therefore, that tanycytes are involved in regulation of the hypothalamic-pituitary-thyroid (HPT) axis and energy homeostasis. To facilitate the study of these cells in neuroendocrine regulation, we will identify tanycyte specific genes by laser capture microdissection and microarray analysis to develop transgenic mice that express Cre recombinase specifically in tanycytes. These mice will be used to develop double transgenic mice in which tanycytes are selectively ablated or marked with GFP to allow isolation by fluorescence-activated cell sorting (FACS) for tissue culture.